For example, glasses-type loupe is known which is worn by a surgeon or a dentist (a medical doctor or the like) to enlarge an affected area where the medical doctor or the like performs surgery. By the way, there is an individual difference in a distance (a working distance) from a worn loupe to a subject which is an affected area, so that it is necessary to adjust the loupe so that focus is adjusted at a working distance suitable to the medical doctor or the like who uses the loupe. Patent Literature 1 discloses a loupe that can adjust such a working distance.
A specific adjustment method of the working distance in Patent Literature 1 is as follows. A rotating barrel that holds an objective lens is screwed with a fixed barrel that holds other lenses including an eye lens around an optical axis, an axial distance between the objective lens and the other lenses is changed according to a phase angle of the rotating barrel with respect to the fixed barrel, and thereby the working distance is adjusted.